@charset "UTF-8";
/*垂直水平居中*/
.a{
    /*文字*/
    height: 10px;
    line-height: 10px;

    /*盒子*/
    position:absolute;
    top: 50%;
    left: 50%;
    transform:translate(-50%,-50%);
    /*flex布局*/
    display:flex;
    justify-content:center;
    align-items:center;
    /*css画出三角形*/
    width: 0;
    height: 0;
    border-left: 50px solid transparent;
    border-right:50px solid transparent;
    border-bottom:100px solid red;
}